1. Field
This invention is in the field of apparatus and methods for testing cylinders in internal combustion engines for compression leaks and for positioning pistons in cylinders in such engines.
2. State of the Art
Most compression leak detectors currently in use include a pressure gauge or other pressure measuring device for quantitatively measuring the pressure built up in an engine cylinder during the compression stroke of the piston in the cylinder as the engine is turned over several times, a device for pressurizing a cylinder and then reading a pressure measuring device to determine how fast pressure is lost, or a device for pressurizing both a chamber to be tested and a similar standard chamber and comparing the change in pressure in the test chamber to the change of pressure in the standard chamber so that temperature changes that can affect pressure measurements are compensated for.
U.S. Pat. No. 4,085,611 shows a hand held gun shaped device connected with a tube having a flexible end plug that is inserted into and held in a spark plug hole in an engine cylinder when the spark plug is removed. The device has a switch which can be operated by the user holding the device to operate the engine starter to turn over the engine. As the engine turns over, the pressure generated in the engine cylinder during the compression stroke of the piston in the engine cylinder is transmitted through the spark plug hole and the tube to a device cylinder in the device. The pressure transmitted through the tube builds up in the device cylinder in the device and acts against a spring loaded piston in the device cylinder to measure the pressure built up in the device cylinder. The pressure built up in the device cylinder is a measure of the compression built up in the engine cylinder and is recorded on a paper chart in the device. The engine is turned over three time for a pressure reading on the third turn over. A valve is provided in the tube from the engine cylinder so that pressure from the engine cylinder can enter the device cylinder but is blocked from escaping. Thus, the pressure is held in the device cylinder until manually released when another engine cylinder is to be tested.
U.S. Pat. No. 3,100,988 is similar in that a pressure gauge has a tube with a rubber stopper at its end that is inserted into and manually held in a spark plug hole in an engine cylinder when the spark plug is removed. The rubber stopper seals the hole. The device has a switch which can be operated by the user holding the device to operate the engine starter to turn over the engine. As the engine turns over, the pressure generated in the engine cylinder is transmitted to the gauge through the tube. The gauge measures the pressure built up in the engine cylinder during the compression stroke of the piston. The engine is turned over several times to get a maximum pressure reading. A valve is provided in the tube from the engine cylinder so that pressure can enter the tube but is blocked from escaping. Thus, the pressure is held in the tube until manually released when another engine cylinder is to be tested. The patent indicates that the pressure in the engine cylinder may be in the order of 125 pounds per square inch (PSI) and that the downward pressure necessary to hold down the rubber stopper in the spark plug hole to maintain a tight seal can be on the order of 100 pounds. With this device and with the device of U.S. Pat. No. 4,085,611, it is difficult for a user to hold the stopper in the spark plug hole to maintain a tight seal against the pressure build up in the engine cylinder to obtain an accurate measurement of the maximum engine cylinder pressure.
U.S. Pat. No. 4,686,851 teaches detecting leakage of a pressure vessel by pressurizing both a test chamber to be tested and a similar reference chamber known not to leak, and then determining if the pressure of the gas in the test chamber changes more over time than the pressure of the gas in the reference chamber. If the pressure of the gas in the test chamber changes more than in the reference chamber (the pressure of the gas in both chambers will generally change due to temperature changes which should be the same for both chambers), the additional change in the test chamber indicates a leak.
U.S. Pat. No. 4,625,545, which was reissued as U.S. Pat. No. RE 33,075, shows a pressure leak detector that pressurizes a test chamber to be tested and then compares the change of gas pressure in the chamber with the rate of change in temperature of the chamber (measured by an infrared detector), the difference in the rates of change being an indication of the test chamber leakage.
With most engines and for most engine repair purposes, it is not important to measure the amount of leakage from a cylinder, i.e., how fast the cylinder leaks, but merely to measure whether the cylinder leaks more than a certain acceptable amount. If leakage is over the acceptable amount, repair is necessary. If under the acceptable amount, no repair is indicated.